Mortuary + Realmwalker + Walking Ballista

Mortuary

Realmwalker

Walking Ballista

How it works

1. Cast Walking Ballista either from your hand or from the top of your library by paying 0.
2. Walking Ballista enters the battlefield and dies as a state-based action due to having zero toughness.
3. Mortuary triggers, putting Walking Ballista on top of your library from your graveyard.
4. Repeat.

By leveraging Realmwalker's ability to choose any creature type via changeling and cast creatures from the top of your library, you can cast Walking Ballista for zero mana. Because Walking Ballista enters with no +1/+1 counters, state-based actions immediately send it to the graveyard, triggering Mortuary to place it right back on top of your library. This creates a continuous loop where you can endlessly recast the automaton, generating infinite creature enters-the-battlefield, leaves-the-battlefield, death triggers, and storm count.